This invention relates to a method of continuously forming high purity glass articles such as tubing and optical waveguide preform. The preform can be severed into discrete draw blanks or continuously drawn into optical fiber.
Generally optical waveguides are made by either outside or inside vapor phase oxidation as hereinafter more particularly defined. In the inside vapor phase oxidation process a coating of glass is deposited on the inside surface of a glass substrate tube. The structure so formed is thereafter heated, the inner hole collapsed, and drawn into an elongated fiber which comprises the optical waveguide. The inner deposited coating of such a process comprises the core of the waveguide while the tubular starting member comprises the cladding. Commercially available glass substrate tubes are generally drawn from a melt and thus contain impurities which result from impure starting materials or impure melting containers. Barrier layers are often deposited in such tubes prior to the deposition of the light-conducting core material to minimize the effect of such impurities on the performance of the resultant optical waveguide fiber.
In the outside vapor phase oxidation process, a starting rod or tube is used as a starting member, bait, or mandrel, on the outside surface of which is deposited one or more layers of suitable material. Ordinarily, the starting member or mandrel is removed leaving the deposited structure as a tubular preform for the subsequent waveguide. The center hole must thereafter be closed before or during drawing, and a solid elongated waveguide fiber is drawn. In the outside process, either the starting rod forms the core of the ultimate waveguide or the first deposited layers form the core of the ultimate waveguide, while the latter deposited layers form the cladding thereof.